I have a question pertaining to the European (I think) rule regarding soft hand double downs, specifically in Pontoon (and BJ for that matter), where doubling down makes the ace count as 1 instead of 11.

Firstly for BJ, double down rule is 9-11 first two cards only. A,8 and A,9 are obviously the only two hands that you could double down on with this rule. Now since these are very strong hands already, is there a point where doubling down on said hands (making them 9 and 10 respectively) is a positive EV decision? I was thinking at least against 5 or 6, with what I'm guessing would have to be a rather high trigger point.

Secondly, Pontoon (which doesn't have redouble by the way). Under basic strategy for Pontoon, and unlike SP21, it doesn't list soft double downs at all. A,2 - A,6 is all hit and A,7 is stand against all dealer upcards unless it's a 9 or higher. But this is where I'm stuck at a theoretical wall; you can double down on any number of cards (as long as its 9-11), there's double down forfeit/rescue and there's also multi-card 21 payouts to consider. However, doubling on soft hands makes the ace count as 1. Given these rules, is there any circumstance where doubling on a natural A,8/A,9 or a multi-card soft 19/20 (so 9/10) is a positive EV decision? What true count would warrant it?

I'm using a modified version of SMC for Pontoon if it helps any.